Read Back Signals in Magnetic Recording - Research Group Fidler

List of Figures
Figure 6.1: The magnetic model used for the FEM calculations. The mesh size for the
shields (green) is 50 nm, and is refined to 5 nm near the track and near the spin
valve layers. The hard bias magnets (purple), the free layer (dark blue), and the
pinned layer (light blue) are also meshed with triangle size of 5 nm..............................66
Figure 6.2: The FEM conductor model is shown. This simplified model shows the four
main layers of a GMR element, which contribute most to the conductance: The
free layer (dark blue) the nonmagnetic Cu layer (orange), the pinned layer (light
blue), and the antiferromagnet (yellow). Additionally the high conductive leads
(pink) are shown..............................................................................................................67
Figure 6.3: The effective conductivities for a typical spin valve taken from [37]. ................68
Figure 6.4: The normalized magnetization of the free layer and the pinned layer in
equilibrium state for the two different current directions. The color code gives the
z-component of the normalized magnetization, red corresponds to the positive and
blue to the negative z-direction. Thus the red arrows represent the pinned layer
magnetization. The right hand side gives the configuration for the more favorable
current direction, because here the current field cancels partially the
demagnetizing field of the pinned layer. .........................................................................69
Figure 6.5: The external applied field, which is applied in z-direction to evaluate the
transfer curve of the GMR sensor. ..................................................................................70
Figure 6.6: The output voltage (left) and the relative change in resistance (right, in
respect to the equilibrium state) over the external applied field in z-direction for
both current direction and a larger exchange bias field...................................................71
Figure 6.7: The transfer curves for the spin valve with and without shields (for both
Hexch = 0.1 T). ..................................................................................................................72
Figure 6.8: The output signal over time for a relaxation from equilibrium state with
Hext = 0.3 T to the equilibrium state without field for different Gilbert damping
constants. .........................................................................................................................73
Figure 6.9: The read back signal and the relative change in resistance for a perfect
→← transition................................................................................................................74
Figure 6.10: The read back signal and the relative change in resistance for a perfect
←→ transition................................................................................................................75
Figure 6.11: The model of a perfect bit pattern. It consists of 30 perfectly written bits
and is used for our read back signal calculations. The track width is 120 nm and
the bit length 60 nm. The layer thickness is 12 nm and the spontaneous
polarization is 0.44 T. The bits are alternately magnetized in positive and negative
x-direction........................................................................................................................76
Figure 6.12: The read back signal for the periodic bit pattern calculated for the GMR
sensor and for the whole read head (with shields). .........................................................76
85